This invention relates to fluid filters and, more particularly, to a pressure relief valve assembly for a spin-on, disposable, oil filter.
Spin-on, disposable, oil filters are used with internal combustion engines to filter out small particulate matter which would otherwise abrade moving engine parts. After a recommended time interval, the filter is replaced and is therefore considered disposable.
Such an oil filter has an outer casing, a filter element disposed within the casing, an end plate fixed to one end of the casing, a pressure relief valve assembly, which enables by-pass of the filter element, when desired, and an antidrain back valve. Plural inlet ports and a central outlet port are provided in the end plate to circulate oil through the filter element. The central outlet port is usually threaded for "spin-on" mounting to the engine.
Relief valve assemblies are known generally to be of two types, metal and plastic.
Examples of metal pressure relief valves are described in U.S. Pat. Nos. 3,473,664, issued to HULTGREN; 4,028,243, issued to OFFER et al.; and 4,497,706, issued to PICKETT et al.
FIG. 1 herein shows a conventional metal pressure relief valve assembly 10 in a filter 11. The filter 11 includes a filter element 22 abutting the pressure relief valve assembly 10 and an antidrain back valve 24.
This pressure relief valve assembly 10 includes a metal upper housing 12 connected to a metal lower housing 14 having oil inlet holes 15 formed radially therein. The upper housing 12 retains a compression spring 16 which urges an annular metal piston 18 and corresponding rubber gasket 20 downwardly into a seated position on the lower housing 14 over the inlet holes 15.
When, e.g. the filter element 22 becomes full of particulate matter, oil pressure at the oil inlet holes 15 increases and eventually overcomes the force of the compression spring 16, causing the gasket 18 and piston 20 to unseat from the lower housing 14. The oil then is allowed to by-pass the filter element 22 and leave the oil filter through the filter element center tube 26 and an oil outlet port 28 formed in an end plate 29.
It is known in the art that the above-described metal valves are relatively expensive to produce due to labor- and energy-intensive metal forming, the relative number of parts and the assembly of these parts, using welding, brazing or soldering. Further, the seal created by the piston 18 and the flat sealing surface of the gasket 20 against the lower housing 14 deteriorates with time due to repeated temperature/pressure cycles.
As indicated above, plastic relief valve assemblies are also known as described in U.S. Pat. No. 3,156,259, issued to HAVELKA et al. and shown in FIG. 2 herein. The valve assembly 30 includes a metal valve plate 32 which is urged into a seated position against a valve body 42 flange 34 including oil inlet holes 36 by a compression spring 38. The spring 38 is biased between the valve plate 32 and hooked extensions 40 which are integrally formed of the valve body 42. The valve body 42 is molded of a plastic material and the flange 34 is also integrally formed therewith. The valve plate 32 is essentially an annular planar member having an inner, upright flange portion 44 which receives radially outwardly the spring 38.
Although HAVELKA et al. indicates the use of a metal piston 32 only, this patent in practice also requires, like the metal valve assembly 10 described above, a molded rubber gasket to effect the desired seal, as is evidenced by subsequent U.S. Pat. Nos. 3,589,517 issued to PALMAI and 4,028,243, issued to OFFER et al. Each of these subsequent patents utilizes the basic HAVELKA et al. relief valve design as well as a rubber piston.
Thus, plastic pressure relief valve assemblies are known to require both a metal piston and gasket, like the metal assemblies. As a result, plastic assemblies suffer from the same drawbacks as the metal assemblies discussed above.
Overall, it is desirous that a relief valve be capable of the lowest cost manufacture and the most efficient sealing properties. For example, having flexibility in choosing the sealing materials and structural design thereof is preferred to being limited to a particular combination of metal and rubber. Finally, it is desirous that a valve assembly be capable of relatively quick and easy automated assembly, requiring no welding, brazing, or soldering.